Executive function deficits in traumatic brain injury

The short and long term pathophysiology of traumatic brain injury (TBI) has not been fully elucidated. Individuals recently suffering a mild TBI (mTBI) or having a history of TBI frequently suffer deficits in their ability to maintain and allocate attention within and between tasks. This dissertation examines the influence of mild and chronic TBI on performance of task switching. We employed spatial and numerical task switching paradigms to assess the behavioral deficits in mTBI, and we used an internally generated switching and an externally cued switching task along with functional Magnetic Resonance Imaging (fMRI) to assess the long term deficits in executive function resulting from chronic TBI.
In the first experiment, individuals with mTBI were identified and tested within the first 48 hours of injury and then at a set interval 5, 14, and 28 days post injury. In the second investigation, individuals with chronic TBI were tested at least 12 months after their most recent injury. Healthy gender, age, and education matched controls were also tested in both studies.
This research demonstrated that mTBI subjects display deficits in switching behavior within 48 hours of injury that failed to resolve a month post-injury; however, these costs did not generalize across the switching task types. Chronic TBI subjects performed internally generated and externally cued switching paradigms with a degree of success equivalent to that of healthy controls but displayed larger amounts of activation and recruited more areas of the brain at lower levels of difficulty and did not increase recruitment in a stepwise fashion at higher levels of difficulty.
Mild TBI causes significant deficits in task switching, but there is specificity in these deficits. Chronic TBI patients performed at a level equivalent to that of controls but displayed different patterns and degree of activation. Taken together, these findings indicate that there may be a specific time frame during which task switching shows behavioral deficits, after which the subject may compensate for these deficits to produce normalized performance.